1. Technical Field
The technology of this disclosure pertains generally to high-throughput communications using error control codes, and more particularly to using variable-length codes with incremental redundancy to approach the Shannon capacity without using feedback to control the transmission of incremental redundancy.
2. Background Discussion
It is well-known that carefully designed error-control codes with very long blocklengths can closely approach theoretical capacity. For example, as demonstrated in 2001 by Chung et al. (“On the design of low-density parity-check codes within 0.0045 dB of the Shannon limit. IEEE Comm. Let., 5(2):58-60, February 2001”), a low-density parity-check (LDPC) code with a blocklength of 107 bits can achieve a bit error rate of 10−6 at a signal-to-noise ratio (SNR) within 0.04 dB of the Shannon limit. However, approaching capacity while simultaneously achieving high throughputs on the order of 100 gigabits per second (Gbps), or more, remains an active area of research.
One example application where high throughput is critical is that of optical transport networks (OTNs). The OTU G.975.1 standard describes forward error correction (FEC) for high-bit-rate dense wavelength division multiple-access (DWDMA) submarine systems. This standard describes “super FEC” schemes that have a higher error-correction capability than the (255,239) Reed-Solomon code, which is the baseline for OTNs. Recent approaches for OTNs include Staircase codes and Braided BCH Codes, which provide significant improvements over the “super FECs” at high throughputs on the order of 100 Gbps. Systems that approach the hard-decoding capacity have been proposed. Spatially-coupled (SC) LDPC codes with windowed decoding provide a possible solution to high-throughput communication systems with soft decoding.
The growing demand for data drives a demand for improved performance over difficult channels. This pushes implementations toward soft decoding and even higher throughputs. Systems constrained to hard decoding cannot approach the soft-decoding capacity. At high throughputs beyond 100 Gbps, the complexity of place-and-route for capacity-approaching schemes, such as iterative belief-propagation decoding of a long-blocklength LDPC code, present a significant challenge. Another factor affecting complexity for soft decoding is that iterative belief-propagation decoders require a larger number of iterations as their operating point approaches the Shannon limit. A third concern is the ability to provide a guarantee on frame error rate (FER) that meets the requirements of high-throughput networks, which sometimes require FERs below 10−15. Guaranteeing low FERs for long-blocklength LDPC codes is difficult as the error-floor behavior of LDPC codes is hard to characterize analytically. Even with windowed SC-LDPC codes, there are concerns about frame error rate guarantees.
High throughputs naturally allow the processing of a large amount of data, which provides the long blocklengths that allow capacity to be closely approached. What is needed is a way to harvest the ergodicity benefits of long blocklengths while somehow achieving the decoder complexity of a short-blocklength code. Feedback allows short blocklength codes to approach capacity, but such feedback is not practical in a high-throughput system.
Accordingly, a need exists for error control mechanisms which operate at high throughputs near capacity. The present disclosure fulfills that need and overcomes drawbacks to previous error control technologies.